Some interactive search functions raise errors when no hit is
found. It is quite annoyning if you have set debug-on-error to t. Is
there any reason why this functions raises errors in this cases? Can
that be used for anything?
An example is the function in the menu bar: Edit - Search - String
Forward. As far as I can see this in only meant to be run
interactively. The same goes for viper-search-next.
It would in my opinion be more convenient if these functions just
return nil and showed a message when a search fails. Would it not be a
good convention for interactive search functions in Emacs?

Probably the better thing to do is to add the error to
debug-ignored-errors.

Oh! Thanks. I was just going to invent that one. How nice it is there
already ;-)

I still believe that interactive search commands should not raise
errors. However I think adding these commands now to
debug-ingnored-errors is the better solution now. Could we please do
that now?